Electric translating apparatus



' Feb. 9, 194 H. w. LORD 2.310.74

ELECTRIC TRANSLATING APPARATUS Filed March 30, 1940 SATURABLE SHUNTSATURABLE can: REACTOI? ngz.

Inventor: Harold, W. Lord,

b )V f w m Hiz zzborney I amnesia. s, 1943 2,310,741 itLl'tCEfB-WJTBANSLA'EING APPARATUS Harold W. Lord, Schenectady, N. 1;, assignor toGeneral Electric Company, a corporation oi New York Application March30, 1940, Serial No. 327,072 25'Claims. (Cl. 176-124);

My invention relates-to electric translating apparatus and more.particularly to improved electric translating apparatus for energizinggaseous discharge devices, such as fluorescent lamps. Certain forms ofapparatus have been devised in the past for converting a low voltagedirect current into an alternating current having the desired highervoltage by employing aninverter including some form of circuitcontrolling means, such as a mechanical commutator, and a transformer.Installations including such apparatus are subject to variousdisadvantages.

With an inverter comprising a part of the apparatus designed to controla group of lamps simultaneously the apparatus lacks flexibility ofcontrol since the use of less'than the full number of lamps constitutingthe group results in an improper operation of the apparatus.

Moreover the weight and cost of such equipment has been excessive,particularly where the number of lamps comprising a group has beenconsiderablyreduced or individual lamp control provided in order .toimprove the flexibility. In certain cases the flicker and stroboscopiceffects produced with such apparatus. have been objectionable.

It is the object of my invention to provide improved apparatus of theabove-mentioned character with which the disadvantages noted may begreatly if not entirely avoided.

It is another object of my invention to provide a new and improvedelectric translating apparatus including switching means for convertingdirect current to alternating current characterized by acurrent waveform in the input circuit having extended periods of low current tofacilitate operation of the switching means and of a substantiallyrectangular current wave shape in the output circuit.

It is a still further object of my invention to provide a new andimproved electric translating apparatus particularly adapted forsupply-- ing electric discharge devices, such as fluorescent lamps.which operates satisfactorily with a variable load and at the same timeovercomes the disadvantages of expense'and weight that result fromsupplying a complete converting system for each individual load device.

improved combined apparatus for energization from a direct currentsource through the contacts of a vibr'atory switch and which includes aninductive device and series resonant circuit which function both toballast the lamp and to draw a current wave throughthe switch contactssuch that sparking is substantially eliminated, this elimination ofsparking being obtained irrespective of whether the lamp'is operatingnormally, is short circuited or is entirely removed.

. The apparatus which I have provided also causes the wave of currentsupplies to the lamp to have a steep slope at the points of reversalwhich in addition to eliminating flicker has a meritorious value inlengthening the life of the lamp.

My invention will be better understood from the following descriptiontaken in connection with the accompanying drawing and its scope will bepointed out in the appended claims.

Referring to the drawing. Fig. 1 is a circuit diagram illustrating anembodiment of my invention and Figs. 2, 3 and 4 show curves of waveforms obtained with the apparatus comprising my invention. In Fig. 1,the source of electrical energy is represented as'the battery 5 whichfor example may be a 32 volt storage battery such as commonly comprisesa part of the lighting equipment of a railway car. The voltage of thebattery is converted into an alternating voltage by means of anysuitable circuit controlling means, which as illustrated, comprises avibratory switch of the reversing type. As I prefer to use a commutatorof the latter type I have shown such a one at 2' having the resilientswitch blades 3 and d which. are tied together and to the driving reed 5by the insulating strip 6. The ends of the blades 3 and t engage thefront and back contacts which connect with the feeder circuit i in themanner of an ordinary reversing switch, the front'and back contacts foreach blade being spaced as short a distance as possible and still obtainsatisfactory operation. The outer or free end of the reed 5 is providedwith 1 the armature 0 which also provides a certain A still furtherobject of my invention is to provide an improved ballast circuit forelectric v discharge lamps which improves the power factor and maintainsgood current wave form through the lamp circuit.

Briefly, inaccordance'with the illustratedembodiment of my invention Ihave provided an amount of inertia and cooperating with the armature 8is the driving magnet iii which receives energy from the battery and iscontrolled by the blades and contacts in a well understood manner tocause the switch arms to operate.

Although the switch arms may vibrate with any desired frequency I preferto so construct it that it. shall operate with a. frequency ofapproximate ly'60 periods per second. The open circuit voltage impressedon the feeder circuit I is represented, for example by the voltage curveA in Fig.

2 in which it will be seen that the short time intervals between thepositive and the negative half cycles are those due to the spacing ofthe front and back contacts of the switch 2.

The feeder circuit 1 is arranged to supply energyto a plurality ofindividually controlled like load circuits, shown as lamp circuits, ofwhich two are represented in Fig. 1. Each lamp circuit supplies anelectric discharge lamp represented at l2 through the apparatus l3 whichserves the double function of ballasting the lamp and causing thecurrent wave'drawn from the source through the switch always to be ofsuch a character that sparking at the switch contacts is avoidedregardless of the functioning of the lamp. The apparatus l3 includes atransformer, which is disclosed and claimed in my copendlng applicationfor Transformer, Serial No. 346,343, filed July 19, 1940, having atwo-part core structure comprising the parts it and which are separatedfrom each other by the air or non-. magnetic gaps IS. The part It isshown of rectangular form having'the primary winding l'l' on the centralleg thereof andhaving the magnetic shunts i8 between the central andouter legs. Each of these shunts comprises two parts, the one partincluding the air gaps formed by the slots i9 and the other partincluding the material below the slot which is adapted to saturateduring the greater part of the current wave traversing the primarywinding. The other part 15 of thetransformer core is shown as having anE-shape with the secondary winding on the center leg thereof.

Connected in series with the primary winding ll to be supplied from thefeeder circuit 1.

through the control switch 2| is the capacitor 22, the winding and thecapacitor forming a resonant circuit tuned to a frequency which isslightly higher than that of the commutator. At

the beginning and at the end of each half cycle 7 of current in theresonant circuit, that is, when the primary current is small thoseportions of the magnetic shunts below the air gap slots are able tocarry the magnetic flux without saturaunder conditions of largevariations of load I have provided the resonant circuit with a nonlinearshunt around the capacitor 22 comprising the saturable core reactor 26and the resistor 21. Under conditions of normal voltage of the,

tion, hence the inductive property of the resonant circuit is relativelyhigh and the resulting resonant frequency of the circuit is low. Duringthe greater portion of each half cycle of the current, however, theshunts are saturated and as a result the inductive property of thecircuit 1; law and the resulting. resonant frequency is In as much asthe natural frequencyof the resonant circuit thus changes during. eachhalf cyazllaitit may be termed a non-linear resonant cir source ofsupply the reactor 26 will operate with a flux density therein which isa little below the point of saturation. However, any material increasein the voltage of the source will cause a saturation of this reactorthereby decreasing impedance of the shunt circuit of which it forms apart to compensate for the effect on the resonant circuit of suchvoltage increase. The shunt moreover prevents any material change in thefrequency of the resonant circuit should the load suddenly change, asfor example, by the removal of the lamp: Thus the shunt circuitincluding reactor 26 and resistor 21 provides means for compensating forchanges in the primary circuit impedance due to voltage changes of thesource as well as compensating for variations in load and may beconsidered a stabilizing circuit.

Referring now to the wave forms comprising Figs. 2 and 3, at the instantthat the switch contacts close in one position thereof, which point isindicated on. Fig. 2 lit-30, an oscillatory current begins to flow fromthe battery, through the commutator, the feeder and the resonant circuitwhich includes the winding l1 and the capacitor. In as much as theresonant circuit is tuned to a frequency slightly higher than that ofthe commutator only the first half cycle of the oscillatory currentpasses before the switch contacts open. The shape of this half cycle isrepresented by B, the times of the closing and opening of the circuit bythe switch being represented respectively by the points 30 and II.During the greater part of this half cycle the shunts I8 are saturated,hence, the inductance of the winding I! at that 'time is relatively low.

the magnetic shunts are able to carry the flux without saturation. Atthese times,.therefore,

The discharge device 'l 2,isconnected in series with the secondarywinding 20 across the capacitor 22 so that theenergy received by thelamp is supplied at various intervals during each cycle of operation bythe secondary winding, and by the capacitor 22 and directly from thefeeder through the primary winding. The discharge lamp may beofanysuitable type and is represented by way 'of example as having heatedelectrodes atthe ends thereof. For the purpose of initially heating theelectrodes before starting the lamp, I have shown by way of example theshort-circuiting switch 24 which is initially closed and after theelectrodes have become heated to an electron emitting temperature isopened thereby causing the lamp to start by reason of the the lnductanceof the winding I! has a higher value, namely, that corresponding to adesaturated condition of the magnetic circuit, The effect of the changefrom one inductance value to another'is to vary the rate .of change oithe current, the eflect being shown by the curved portions 32 and uofthe current wave. The rate of change of the current finally reaches avery low value represented by the flat portion 34 of the curve, see Fig.3, into which the curved portion 33 merges. In this figure I haverepresented on a larger scale the form that the curve B would take inthe zero part thereof were the circuit not opened by the switch. Thecurrent passes throughzero in this flat portion which portion makes sucha small angle with the zero axis that for an appreciable interval beforeand afterthe time of actual zero value the current is practically zero,in fact is so 'small that only a minute spark if any is produced it thecircuit is opened at any instant during that interval,

with the apparatus which I have devised the opening of the circuit bythe switch may therefore occur at any point along the flat portion 34 ofthe current curve, for example anywhere bee tween the points 38 and 39of Fig. 3 without;

causing detrimental sparking at the switch, con-' is provided to insureagainst switchsparking by reason of'small variations that may occur inthe frequency of the switch and the resonant circuit and in thestructural features of the apparatus. When the switch contacts close inthe other position, as at the point 35, in Fig. 2, a

'similar half cycle of current but of the opposite polarity, indicatedat B, is drawn from the battery through the commutator, the interruptionof the current at the end\of eaeh half cycle occurring at acorresponding point in the flat portion 34 of the current wave. Curve Cdrawn to a differentscale than that of the curve B, represents the waveform ofthe current flowing through the lamp which current is suppliedprincipally by the secondary winding of the transformer but during theintermediate portion thereof, approximately between the points 1 it'willbe apparent that various modifications may be made withoutdeparting from the spirit,

. and scope of my invention which modifications I aim to cover by theappended claims.

' What I claim as new and desire to secure by Letters Patent of theUnited States is:

1. In combination, a source of direct current supply, a commutatorconnected therewith for producing a substantially square shapedalternating voltage wave having zero voltage po'rtions between thehalf-cycles thereof, a discharge lamp connected to be supplied from saidcommutator and apparatus in said connection including means forballasting said lamp and means including a resonant circuit and a corehaving a saturable partv associated therewith for causing thealternating current drawn from said commutator to pass through zero at adecreased rate of change, the interval of said decreased rate of changeincluding the time of interruption of the circuit by the. commutator andmeans for maintaining the operation of said resonant ,cir- I cuitsubstantially independent of the functioning of the lamp.

2. In combination, a sourceof direct current supply, a commutatorconnected therewith for 36 and 31, is supplied by the capacitor 22. ,Thea gaps 16 between the core structures associated with windings H and 20.maintain the exciting reactance of winding 20 at a relatively low value.This renders it possible for the. capacitor 22 to maintain a substantialcurrent through the load circuit during open circuit condition of thepri marywinclingoccurring during movement of the movable switch contactsfrom one closed circuit position to another. It is apparent that some ofthe features of the transformer capacitor combination of the illustratedembodiment of my invention may be utilized to advantage as a ballastcircuit for discharge devices such as fluorescent lamps when energizedfrom a sinusoidal alternatingvoltagesource as wellas from a commutateddirect current supply as illustrated in the drawing. It will be notedalso that this lamp current curve C is very steep where it ing from anoutputcu'rrent curve having such a steep slope is the substantialelimination of lamp flicker and an increase in lamp life. I

The curves B and B represent the curren waves drawn fromthe feeder withthe lamp in normal operation. Should the lamp'be removed or renderedinoperative the current curve would then become somewhat more peakedsuch as is represented, for example, by the curve B'Fof Fig. 4. Althoughthe current, under such -conditions is more peaked than under the normallamp operating condition that portion of the current curve adjacent thezero axis, namely the fiat portion, is substantially the same. Moremainssubstantially the same when the lamp is short circuited by the startingswitch. Thus the production of a flat portion in the current wave whereit passes through zero and the positioning of that portion to includethepoint of interrupproducing 'a substantially square shaped alternatingvoltage wave having zero voltage portions between the-half-cyclesthereof, a resonantcircuit directly. connected with said commutator andhaving a frequency higher than that of said voltage wave connected to beenergized thereby, an electrical load connected to be energized from anelement of said circuit, and means including a core having a saturablepart cooperating with said circuit for causing each current wave thereinto have a flat portion where the wavegpasses through zero, the timeinterval represented by said fiat portion including the time at whichthe commutator opens the circuit, said resonant circuit including meansoperative to maintain the frequency of the circuit substantially uniformover wide ranges, of variation of saidload.

- t 3. In combination, a source of direct current a supply, a commutatorconnected therewith for producing a substantially square shapedalterhating voltage wave having zero voltage portions between the halfcycles thereof, means for con-= I,

necting a discharge lampto be supplied from said commutator andapparatus in said connection comprising a transformer having a parttened portion where it'passes through-zeroinproducing a substantiallysquare shaped alterin over, that portion of the current curve also re-v5 dependent .ofthe opeif ing of the contacts, the time of interruption othe current by the commutator occurring; during said flattened portion.

A In combination, a source of direct'current supply, a commutatorconnected therewith for nating voltage wave having zero voltage portionsbetween the half cyclesthereof, a trans-' former having a core structureproviding a non,-

magnetic gaping the flux path interlinking the n tion of the switch issubstantially independent of the functioning of the load.

I have chosen the particular embodiment described above as illustrativeof my invention and 7 primary and secondary windings thereof andproviding a magnetic shunt between said wind-Y ings, said .shunt 'havinga-saturable portion and anonmagnetic gap arranged in parallel, 9. cavpacitor connected in series with saidprimary winding to be suppliedfromsaid commutator and forming a resonant circuit. a discharge lamp,andmea'ns connecting said lamp and-said secondary winding in seriesacross said capacitor.

5. In combination, a source of direct current supply, a commutatorconnected therewith for producing a substantially square shapedalternating voltage wave having zero voltage portions between the halfcycles thereof, a transformer having a core structure providing an airgap in the flux path interlinking the primary and secondary windingsthereof and providing a magnetic shunt between said windings, said shunthaving a saturable portion and an air gap arranged in parallel, acapacitor connectedin series with said primary winding to be suppliedfrom said commutator and forming a resonant circuit, a discharge lamp,means connecting said lamp and said secondary winding in series acrosssaid capacitor and means for compensating for the effect on saidresonant circuit of an increase in voltage of the source comprising acircuit including a saturable core reactor connected across saidcapacitor.

6. In combination, a source of direct current supply, a commutatorconnected therewith for producing a substantially square shapedalternating voltage wave having zero voltage portions between thehalf-cycles thereof, a feeder circuit connected to be supplied from saidcommutator, and a plurality of lamp circuits connected to be suppliedfrom said feedercircuit and each including a discharge lamp, controlapparatus and a control switch in the connection between the lamp andthe feeder circuit, each of said control apparatus including means forballasting the lamp associated therewith and means including a resonantcircuit and a core having a saturable part associated therewithoperative independently of the functioning of the lamp to cause thecurrent drawn from said commutator to pass through zero at a decreasedrate of change, the time of interruption of the circuit by thecommutator occurring during the interval of said decreased rate ofchange whereby sparking at the commutator contacts is avoided regardlessof the occurrence of 'small variations,

in the separate lamp circuits.

7. In combination, a source of direct current supply, a commutatorconnected therewith for producing a substantially square shapedaltertions between the half-cycles thereof, a transformer including aprimary winding, a secondary winding and a core structure, a resonantcircuit directly connected with said commutator and including acapacitor and a winding of said transabove a predetermined value forcausing each half cycle of current in the circuit to have a nected forenergization from a reactive element of each resonant circuit,connecting means for supplying said resonant circuits in parallel fromsaid direct current circuit, common switching means in said connectingmeans for periodically reversing the polarity of the direct currentpotential supplied from said supply circuit to said resonant circuits,and means for operating said switching means at a frequency slightlylower than the frequency of said resonant circuits.

10. In combination, a source of direct current, an electric dischargedevice, electric translating apparatus interconnecting said source andsaid discharge device comprising transformer means including a primarywinding and a secondary winding, circuit controlling means interconnect-,ing said source and said primary winding for periodically energizingsaid primary winding, a condenser electrically connected with one ofsaid windings for tuning the circuit of the primary winding'tosubstantially the frequency of operation of said circuit controllingmeans, and a stabilizing circuit responsive to the voltage of saidcondenser for maintaining the tuning of vsaid primary circuitsubstantially independent of circuit controlling means, andregulatingmeans 'nating voltage wave having zero voltage porflat portionwhere the wave passes through zero.

8. In combination. a source of direct current, a plurality of resonantcircuits, a separate load circuit connected to be energized from each of7 .that, ofsaid resonant circuits.

7 9. A direct current supply circuit, a plurality of series resonantcircuits each comprising a pluing said source and said primary winding,means for operating said circuit controlling means periodically toenergize said primary winding, capacitance means associated with one ofsaid windings for tuning the circuit of said primary winding tosubstantially the frequency of operation of said circuit controllingmeans, and a stabilizing circuit connected with said secondary windingfor rendering the tuning of said circuit substantially independent ofthe functioning of said discharge device or variations of said sourcevoltage comprising a saturable inductance device and resistance elementconnected in series.

13. In combination, a source of direct current, a plurality of seriesresonant circuits, a plurality of separate electric energy consumingloads each energized from one of said resonant circuits, commonswitching means interconnecting said 7 circuits and said-source ofdirect current, means rality of reactive elements, a load circuit con-76 for operating said switching means to energize said resonant circuitsin parallel at substantially the frequency of oscillation of saidresonant circuits.

14. A direct current supply circuit, an alternating current loadcircuit, electric translating apparatus interconnecting said circuitscomprising transformer means including a primary and a secondarywinding, circuit. controlling means interconnecting said direct currentsupply circuit and the primary winding of said transformer device forperiodically energizing said transformer primary winding, andcapacitance means conductively associated with both said primary andsaid secondary windings for receiving and storing energy when saidprimary winding is energized from said supply circuit and for supplyingenergy to the circuit of said secondary winding during the period thatsaid circuit controlling means is eirective to open the circuit betweensaid supply circuit and said primary winding to maintain substantialcurrent flow in said secondary winding during open circuit of saidprimary circuit.

15." A direct current supply circuit, an alternating current loadcircuit, electromagnetic means and circuit controlling meansinterconnecting said circuits, means for controlling the energizeperiodically said electromagnetic means from said supply circuit toeffect an electromagnetic transfer of energy between said supply circuitand said load circuit, and capacitance means conductively associatedwith saidelectromagn'etic means and cooperating therewith to reduceperiodically the current through said circuit controlling means to zeroand to supply energy to said load circuit for aperiod in each cycle ofcurrent in said load circuit including the period of zero currentthrough said circuit controlling means.

16. A direct current supply circuit, an alternating current loadcircuit, electric translating windings, switching ,means forperiodically energizing said primary winding from said direct operationof said circuit controlling means to minal or said load circuit, andcircuit controlling means operable to connect periodically the otherterminal of said condenser and the terminal of said primary windingremote'from said common terminal withsaid direct current supply circuit.

19. Electric translating apparatus for supplying an alternating currentvoltage to a load having the characteristics of an arc dischargedevice'i'rom a direct current source comprising a transiormer includinga primary winding, a secondary winding and a core structure for saidcurrent source 'to produce an alternating current fluxin said corestructure, means for maintaining the primary current at a relatively lowvalue over a prolonged period near the beginning and end or each haltcycle comprisins a magnetic shunt arranged between said windings andhavingparallel saturable and nonsaturable portions,

' and means for maintaining a substantially even apparatusinterconnecting said circuits comprising transformer means having a'primary winding and a secondary winding, circuit controlling meansconnectedin circuit with said primary I winding andoperative-periodically to connect said primary winding with said directcurrent supply circuit, a capacitance conductively connected with atleast one of said windings for maintaining a current through saidsecondary winding during periods of zero current in said primary windingoccurring during circuit interrupting operation of said circuit,controlling means, and means for maintaining the impedance of saidsecondary winding at a low value when the circuit of saidprimarywindingis interrupted.

17. A direct current supply circuit, an alternating current loadcircuit, electric translating apparatus interconnecting said circuitscomprising transformer means having a primary winding and a secondarywinding, mechanical switching means interconnecting said primary windingand said direct current supply circuit, means for operating saidswitching means to open and close said primary circuit periodically, acapacitance connected with said secondary winding for maintaining acurrent therethrough during the periods that said switching means is inthe open circuit position, and means including a nonmagnetic gap; in themagnetic circuitlinking said pri- 'mary and secondary windings formaintaining the impedance of said secondary winding at a low valueduring the period that said switching 7 means is in'open circuitposition.

18. A direct current supply circuit, an alternating current loadcircuit, electric translating apparatus interconnecting said circuitscomprising a transformerdevice including primary and secondary windingshaving a common terminal,

capacitance means having one terminal thereof flow of secondary currentduring the period or reduced primary current including a nonmagnetic gapin the local magnetic circuit of said secondary winding. a Y

20. A direct current supply circuit, an alternating current loadcircuit, electric translating apparatus interconnecting said circuitscomprising inductive means-having a plurality oi windf ing sections. andincluding a core structure having a saturable portion for introducing anonlinear current impedance characteristic in said translatingapparatus, circuit controlling means for periodically connecting saidtranslating apparatus'with said'direct current supply circuit, and acondenser associated withsaid winding sections and cooperating therewithto provide a series resonant circuit having a ireguency slightly'higherthan the pe iod of operation of said circuit controlling means when thesaturable portionof said core structure is saturated to produce anoscillatingcurrent throughsaid controlling means having extended periodsof low current at the times of operation of said current controllingmeans, said capacitance means also cooperating with said inductivedevice to mainconnected with said common terminal and the otherterxninalthereof connected with one tertain a substantial current through saidload circuit during the extended periods of low current through saidcircuit controlling means.

V 21. A directcurrent supply circuit, an alternating current loadcircuit, electric translating apparatus interconnecting said circuitscomprising inductive means having a plurality-oi winding sections andincluding a core structure having a saturable portion for introducinganon- 'linear current impedance characteristic in said operation of saidcircuit controlling means, a

nonmagnetic gap in said core structure in the magnetic circuit linkingsaid, winding sections operable to maintain the impedance of one of saidwinding sections at a low value when the other 'oiv said windingsections is open circuited by operation of said circuit controllingmeans to reverse the connection between said translating apparatus andsaid supply circuit, said capacitance means cooperating with said one ofsaid winding sections to maintain a substantial current through saidload circuit during the period that said switching means isin opencircuit position.

22. In combination, a source of alternating current voltage, electrictranslating apparatus energized from said source for ballasting anelectric discharge device comprising a transformer including a primarywinding, a secondary winding and a core structure constructed to provideshunt between said windings, a capacitor connected in series with saidsecondary winding and a nonmagnetic gap in the series magnetic circuitof said primary and secondary windings.

24. In combination, a source oiperiodic volt-v age, an electricdischarge device. electric translating apparatus interconnecting saidsource and said device comprising transformer means including a primarywinding and a secondary winding, a condenser electrically connected withquency of said periodic voltage, and a stabilizing circuit connectedacross said condenser for maintaining the tuning of said primary circuitsubstantially independent of the operation 01' sai discharge device.

25. In combination, a direct current supply circuit, a transformerincluding a primary winding, a secondary winding and a core structure, adischarge lamp connected with said secondary winding, mechanicalswitching means interconnecting said supply circuit and said primarywinding, means tor operating said mechanical switching means to energizesaid primary winding with a periodic voltage, and means for regulatingthe primary current to minimize sparking mat the contacts of saidmechanical switching means comprising a magnetic shunt extending betweensaid windings and having parallel saturable and nonsaturable portionswith said saturable portion designed to be unsaturated durin a period oftime including the operating time oi said mechanical switching means andsaturated during the remainder of each cycle or said periodic voltage.

. HAROLD W. LORD.

